1. Field of the invention
This invention relates in general to oil, water and gas wells, and in particular to a means for handling low pressure gas produced in a well by the use of a downhole gas compressor.
2. Description of the Prior Art
Electrical submersible pumps are commonly used in oil wells. Electrical submersible pumps have found particular applications in wells which produce a large ratio of water relative to the oil, and wherein the formation pressure is not sufficient for the well to flow naturally. A typical electrical submersible pump is centrifugal, having a large number of stages of impellers and diffusers. The pump is mounted to a downhole electrical motor and the assembly is supported in the well on production tubing. A power cable extends alongside the tubing to the motor for supplying power from the surface.
In some instances, a well will also produce quantities of gas along with the liquid. Centrifugal pumps are designed for pumping incompressible liquids. If a sufficient amount of gas is present, the pump will lose efficiency because gas is compressible. Gas separators have been employed to reduce the amount of gas entering the centrifugal pump. A gas separator separates a mixture of liquid and gas by centrifugal force. The liquid flows through a central area into the intake of the pump. The gas is discharged out gas discharge ports into the annulus surrounding the pump. Gas in the annulus collects at the surface of the well and is often introduced through a check valve back into the production flowline at the surface.
Electrical submersible pumps cannot be employed if a well produces principally gas. Gas wells are normally produced by their own internal drive due to the formation pressure. In some instances, however, the gas flow is inadequate either due to poor permeability or low pressure. In these instances, generally the wells are not produced.
Gas compressors, of course, have been known in general in industry. Centrifugal gas compressors utilize stages of rotating impellers within stators or diffusers. However, the design is such that they will operate to compress gas, not pump a liquid. Generally, a centrifugal gas compressor must operate at a much higher rotational speed than a liquid pump. To applicant's knowledge, downhole gas compressors have not been employed in connection with producing gas from a well.